Subject: Re: [PATCH 2/3] replace-objects: create wrapper around setting

From: Victoria Dye <[email-masked]>
Date: Thu, 1 Jun 2023 09:35:40 -0700

Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <[email-masked]>
> 
> The 'read_replace_objects' constant is initialized by git_default_config
> (if core.useReplaceRefs is disabled) and within setup_git_env (if
> GIT_NO_REPLACE_OBJECTS) is set. To ensure that this variable cannot be
> set accidentally in other places, wrap it in a replace_refs_enabled()
> method.
> 
> This allows us to remove the global from being recognized outside of
> replace-objects.c.
> 
> Further, a future change will help prevent the variable from being read
> before it is initialized. Centralizing its access is an important first
> step.
> 
> Signed-off-by: Derrick Stolee <[email-masked]>
> ---
>  commit-graph.c   |  4 +---
>  environment.c    |  1 -
>  log-tree.c       |  2 +-
>  replace-object.c |  7 +++++++
>  replace-object.h | 15 ++++++++++++++-
>  5 files changed, 23 insertions(+), 6 deletions(-)
> 
> diff --git a/commit-graph.c b/commit-graph.c
> index 43558b4d9b0..95873317bf7 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -203,14 +203,12 @@ static struct commit_graph *alloc_commit_graph(void)
>  	return g;
>  }
>  
> -extern int read_replace_refs;
> -
>  static int commit_graph_compatible(struct repository *r)
>  {
>  	if (!r->gitdir)
>  		return 0;
>  
> -	if (read_replace_refs) {
> +	if (replace_refs_enabled(r)) {
>  		prepare_replace_object(r);
>  		if (hashmap_get_size(&r->objects->replace_map->map))
>  			return 0;

This and the other 'read_replace_refs' -> 'replace_refs_enabled()'
replacements all look good. Although we're not using the 'struct repository'
argument yet, I see that it'll be used in patch 3 - adding the (unused) arg
here helps avoid the extra churn there.

> diff --git a/replace-object.c b/replace-object.c
> index ceec81c940c..cf91c3ba456 100644
> --- a/replace-object.c
> +++ b/replace-object.c
> @@ -85,7 +85,14 @@ const struct object_id *do_lookup_replace_object(struct repository *r,
>  	die(_("replace depth too high for object %s"), oid_to_hex(oid));
>  }
>  
> +static int read_replace_refs = 1;
> +
>  void disable_replace_refs(void)
>  {
>  	read_replace_refs = 0;
>  }
> +
> +int replace_refs_enabled(struct repository *r)
> +{
> +	return read_replace_refs;
> +}
> diff --git a/replace-object.h b/replace-object.h
> index 7786d4152b0..b141075023e 100644
> --- a/replace-object.h
> +++ b/replace-object.h
> @@ -27,6 +27,19 @@ void prepare_replace_object(struct repository *r);
>  const struct object_id *do_lookup_replace_object(struct repository *r,
>  						 const struct object_id *oid);
>  
> +
> +/*
> + * Some commands disable replace-refs unconditionally, and otherwise each
> + * repository could alter the core.useReplaceRefs config value.
> + *
> + * Return 1 if and only if all of the following are true:
> + *
> + *  a. disable_replace_refs() has not been called.
> + *  b. GIT_NO_REPLACE_OBJECTS is unset or zero.
> + *  c. the given repository does not have core.useReplaceRefs=false.
> + */
> +int replace_refs_enabled(struct repository *r);

Since the purpose of this function is to access global state, would
'environment.[c|h]' be a more appropriate place for it (and
'disable_replace_refs()', for that matter)? There's also some precedent;
'set_shared_repository()' and 'get_shared_repository()' have a very similar
design to what you've added here.